1. Field of the Invention
The present invention relates to methods, reagents, and kits for assessing organ damage, such as damage due to ischemia reperfusion injury, in the course of a transplantation therapy and/or for assessing organ regeneration following transplantation therapy.
2. Description of the Related Art
The central focus of organ transplantation therapy has been the prevention of acute rejection. (See for example, The Handbook of Transplantation Management by Leonard Makowka, CRC Press, 1991.) In attempting to prevent acute rejection, therapies have evolved to reduce or to control the appropriate recognition of allopeptides by helper T cells. As a result, early rates of acute rejection have lowered to below 20% and increased one-year renal allograft survival to well above 80%. Unfortunately, this improved early graft survival has not translated to improved long-term graft survival. Graft half-life and the effects of chronic allograft nephropathy have remained relatively constant throughout the eras of calcineurine inhibition and monoclonal antibody therapies.
Survival of any organ or cell is dependent on the availability of oxygen and crucial nutrients and removal of cellular waste. Metabolic processes must function in a balanced manner to maintain cellular homeostasis. Disruption of this critical balance by physical, chemical or oxidative stress results in changed rates and direction of normal biochemical and molecular reactions as the cells attempt to maintain cell functions and adapt to stressful conditions.
Oxidative stress is induced by the total stoppage of blood flow (ischemia) incident to the removal of an organ from a donor, cold storage, warming, and re-implantation into a recipient in the course of transplantation and results in a fundamental metabolic imbalance. Switching from aerobic to anaerobic conditions results in an accumulation of harmful substrates and stimulation of catabolic pathways to eliminate undesirable metabolic byproducts. This metabolic imbalance continues as long as a lack of oxygen lasts. Ultimately, diminished metabolic rates, metabolic acidosis and calcium and sodium overloading accelerate cell and organ death. Reperfusion, resumption of oxygenated blood flow to an ischemic organ, intensifies injury by providing conditions that activate free radical production and a cascade of reactions leading to recruitment and activation of neutrophils and platelets. Organ damage caused in this process is known as ischemia reperfusion injury (IRI).
With respect to kidney transplant, it is known that cold storage may cause delayed graft function (DGF), which in turn causes reduced short and long term renal allograft survival (Ojo, et al., Transplantation, 63:968-974, 1997). However, while prolonged cold ischemia is known to have detrimental effects on graft survival, the cellular and molecular responses of the kidney to ischemic insult are not completely understood. Various experimental studies have tried to determine the mechanisms involved in acute ischemic renal failure. See, for example, a review by Sheridan and Bonventre (Curr. Opin. Nephrol. Hypertension, 9:427-34, 2000).
Its remarkable regeneration potential enables the kidney to completely restore its function and to replace damaged cells and to restore epithelial continuity. However, in different situations, recovery is delayed or does not occur at all. The mechanism underlying the detrimental effect of cold ischemia and thermal injury on graft survival remains unclear and the factors that trigger and control the repair process are poorly understood. For background on kidney disease including theory and practice known to one of skill in the art, see Disease of the Kidneys (6th Ed.) by Robert Schrier and Carl Gottschalk, Little Brown and Company (1996).
Currently, assessment of renal graft dysfunction following transplantation relies on the measurement of plasma creatinine and the often inconclusive histological results of a renal biopsy. In addition, the results of such measurements are essentially descriptive and are not effective predictive markers.
Therefore, the art is in need of improved methods for the assessment of organ health in the course of transplantation therapy, for outcome prediction, and for the assessment of regeneration following transplantation therapy. These and other objects are provided by the present invention.